A stress and strain sensitive oscillator with sensing and actuator applications
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All magnetoelastic effects have an inverse. When a strain is applied to a magnetostrictive material there is a magnetic effect and when a magnetic field is applied there is a strain. The ‘Vibe’ project came about as a side project carried out at MagCanica. Ivan Garshelis and Ryan Kari were pondering what was the inverse of a magnetoelastic force transducer invented by Ivan several years ago.
The bending sensor demonstrated that when a bending moment is applied to a circumferentially magnetized tube, a change in the measurable magnetic field can be detected outside of the shaft. This brought up the question, “what happens when a magnetization is applied to a tube that is acted upon by a bending moment, and in particular a circumferential magnetization such as that produced by electrical current conducted through a wire?” What we learned was there is a fundamental magnetoelastic effect that was never before described that might have great utility – perhaps it could be called the Garshelis and Kari Effect, but we prefer just to call it Vibe.
The objective of this website is to describe the journey and teach our understanding of what this magnetoelastic effect is. We do this through included videos, descriptions, and thought experiments. These include focusing on fundamentals, but also exploring particular arrangements to demonstrate the different utilities from both the perspective of using the effect to act as an actuator and also to act as a stress sensitive sensor, such as that presented here.
Although progress isn’t expected to be quick, we also intend to share the most recent activities and results when we continue to explore this phenomenon. While we don’t know of the ideal practical applications of such an effect, the world is a big place such that our goal is simply to inform you, the reader.
Applications
There are possible applications to both actuation and sensing. What follows will be an overview of how the phenomenon can be harnessed to induce motion but also use the motion induced to provide a means of sensing a secondary parameter, such as deflection, strain, or even a change in mass.
Sensing
The unique attribute
is that the magnitude of the effect is dependent on the strain (or stress)
available to be acted upon.
If there is no strain component, applying a magnetization will not do anything.
The greater the strain component, the greater the effect of the magnetization.
This makes it possible to use this attribute as an oscillator that is dependent on the strain present, such that strain can be measureable.
An example of this is shown in the video. A cantilever is fixed at both ends, in which one end is on a linear stage that can be displaced in the vertical direction. This results in strain being placed into the cantilever and the deflection curve changing. An optical emitter / detector pair is configured to detect the position of the cantilever at one location. Amplification and filtering electronics amplify this signal and send it to a Microchip microcontroller (dsPIC33F), which carries out a control loop and is configured to send a pulse of current in phase with the oscillation of the beam, allowing it to sustain its oscillation. If there is more deflection (stress) for the magnetic field induced by current to act on, there is more ‘kick’ creating a greater oscillatory magnitude. The video walks through the setup, in which the oscillatory frequency is too high to see, but can be heard at 540Hz (close to C5 on a piano). This matches the expected resonance frequency that can be provided from sources such as The Machinery’s Handbook or sites such as Engineer’s Edge.
Actuation
The most direct actuation is that of the vibrating cantilever itself. It is expected that about 2 to 4% of the total strain present can be converted into strain through a magnetic excitation. The amount of current and thus power required to produce this excitation will be dependent on resistivity, crystal anisotropy, and magnetostriction. A visible example of this can be seen in the following video, in which current is being pulsed through the cantilevered beams which are supporting an ~1 lb weight. The feedback signal is originating from a magnet inducing a voltage in a search coil.
The unique attribute is that motion is produced entirely within the structure of the wire itself. However, how is the motion to be converted into useful motion such as rotary or linear? Inspiration might be taken from piezoelectric actuation and in particular the bimorph principle. “A bimorph is a cantilever used for actuation or sensing which consists of two active layers.” A great picture is shown on Wikipedia here.
Thought experiment
A thought experiment carried out several years ago. I assumed I was locked in a tower and had to devise of a way to measure flow with the Vibe concept before being able to get out . While there are many means of measuring flow, we wanted to think of an unconventional means. Ivan taught me to always begin by being locked in a tower when carrying out thought experiments…
Direct
The first method would involve placing a member directly into the flow, which would act to bend the member. The more flow, the more moment acting on the cantilevered member, and the more the cantilever would respond to an applied magnetic field acting on it (the assumption is the flow is compressible such that it wouldn’t prevent / impede deflection significantly). The resonance frequency could then be measured in which the amplitude at the resonance frequency would be a function of the flow.
Separate member
A variation of this, a separate member could be rigidly attached to the member in the flow (without being in the flow itself). As the member in the flow bends, if rigidly attached, a portion of the strain would flow through the secondary member. This secondary member could use the Vibe principle , in which the amplitude of oscillation at its resonance frequency would be a function of the flow.
Integrated portion
A third variation of this, is the same member within the flow could use an integrated portion as the active region. This could be represented either as a portion of the member in series, or even more complicated assemblies that use a multitude of beams connected together to condition the strain to be best suitable for the Vibe principle.
Position measurement for feedback
In each of these cases, the position could be measured using any number of techniques, such as a laser interferometer, typical optical emitter detector pair such as this provided by Vishay, capacitive as measured between a parallel plate not being deflected, or even as a measurement of the reactionary force acting on the base just to name a few. Alternatively, we also demonstrated that signals within the beam itself based on the changing magnetization (induced from motion) could act as the signal itself. I haven’t yet provided a description of this nor data, but will in the near future.
Summary
While these ideas are relatively simple, they can certainly be expanded beyond flow and teach that: (i) the cantilever itself can be used, (ii) a portion of the cantilever can be used as the active region, or (iii) a separate member can be used as a sensor and attached to something carrying the load. If a flow can be measured, so can any type of strain or stress, potentially on nearly any scale.
